Sealants are used to isolate an environment, serving as a barrier to the passage of gases, liquids, and solid particles. Sealants also serve to attenuate mechanical shock, vibration, and sound, maintain a pressure differential, and protect items mechanically, electrically, and thermally.
The largest use of sealants is in commercial and home construction and repair, and in the transportation market. Exterior commercial construction sealants must accommodate large changes in joint gap or width from temperature cycling and wind loads. In addition, the sealants must resist rain, heat, ultraviolet light, oxygen, and ozone. Building materials such as concrete, stone, marble, aluminum, steel, glass, and plastics differ widely in thermal coefficients of expansion, so joint design is very important for sections of different materials that are fitted together. The gap width between sections is based on material type and length of section, with a wider gap for larger sections. Sealants are also commonly used for expansion joints in parking decks.
Polyurethanes have suitable properties for many useful products, including elastomeric sealants prepared from the reaction of hydroxy-functional components with isocyanate-functional components. Polyurethanes have utility as high performance sealants which are suitable for commercial building and construction for interior and exterior sealing. High performance sealants can typically accommodate significant joint movement in compression or tension with good recovery.
Single-part polyurethane sealants typically are produced by reacting a polyol with a polyisocyanate, with or without a catalyst, in a reactor for up to eight hours to produce an isocyanate-terminated prepolymer. Various additives are blended with the prepolymer to provide a product having the desired characteristics and the resulting product is packaged in substantially hermetically sealed containers for use.
Regulatory requirements require reduction in the volatile organic compounds (voc) content of sealing materials such as joint sealants. To meet these ever-increasingly stringent standards, volatile solvent content must be reduced. However, volatile solvents serve useful purposes in sealing materials such as viscosity reduction, improvement of handling, and ensuring quick tack-free drying times.
Therefore a material is needed to replace volatile solvents so as to reduce volatile organic compounds (voc) in sealing materials without affecting the processability, handling, and package stability. What is also needed are low volatile organic compounds materials that have little color or smell and do not affect the long term package stability.